Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.74   13.659%   $233.842   $233.84   $233.85   $233.80  
  Purchase #2 $67.29   13.318%   $76.2517   $76.25   $76.25   $76.30  
  Purchase #3 $38.38   10.772%   $42.5143   $42.51   $42.50   $42.50  
  Purchase #4 $201.74   5.152%   $212.1336   $212.13   $212.15   $212.10  
  Purchase #5 $40.66   3.187%   $41.9558   $41.96   $41.95   $42.00  
  Purchase #6 $117.79   9.474%   $128.9494   $128.95   $128.95   $128.90  
  Purchase #7 $154.51   9.807%   $169.6628   $169.66   $169.65   $169.70  
  7 purchase totals = $826.11       $905.3096   $905.30   $905.30   $905.30